1. Field of the Invention
The present application relates to a compressed natural gas injector, which incorporates an improved low noise valve needle.
2. Description of the Related Art
Compressed natural gas (hereinafter sometimes referred to as "CNG") is becoming a common automotive fuel for commercial fleet vehicles and residential customers. In vehicles, the CNG is delivered to the engine in precise amounts through gas injectors, hereinafter referred to as "CNG injectors". The CNG injector is required to deliver a precise amount of fuel per injection pulse and maintain this accuracy over the life of the injector. In order to maintain this level of performance for a CNG injector, certain strategies are required to help reduce the effects of contaminants in the fuel.
Compressed natural gas is delivered throughout the country in a pipeline system and is mainly used for commercial and residential heating. While the heating systems can tolerate varying levels of quality and contaminants in the CNG, the tolerance levels in automotive gas injectors are significantly lower.
These contaminants, which have been acceptable for many years in CNG used for heating, affect the performance of the injectors to varying levels and will need to be considered in future CNG injector designs. Some of the contaminants found in CNG are small solid particles, water, and compressor oil. Each of these contaminants needs to be addressed in the injector design for the performance to be maintained over the life of the injector.
The contaminants can enter the pipeline from several sources. Repair, maintenance and new construction to the pipeline system can introduce many foreign particles into the fuel. Water, dust, humidity and dirt can be introduced in small quantities with ease during any of these operations. Oxides of many of the metal types found in the pipeline can also be introduced into the system. In addition, faulty compressors can introduce vaporized compressor oils, which blow by the seals of the compressor and enter into the gas. Even refueling can force contaminants on either of the refueling fittings into the storage cylinder. Many of these contaminants are likely to reach vital fuel system components and alter the performance characteristics over the life of the vehicle.
In addition to contaminants in the CNG, presently known valve components of fuel injectors have been known to present certain disadvantages, when used with CNG as well as with liquid fuels. For example, the armature and valve needle of a typically known injector produces distinguishable sounds upon opening of the valve and on closing of the valve. In particular, the force of impact, which is equal to the valve component mass multiplied by acceleration, can generate sounds within an engine compartment, which are generally perceived as either a mechanical problem or otherwise harsh and objectionable noise.
In general, fuel injectors require extremely tight tolerances on many of the internal components to accurately meter the fuel. For CNG injectors to remain contaminant tolerant, the guide and impact surfaces for the armature needle assembly require certain specifically unique characteristics. Also, the valve needles are difficult to control precisely, given the specific environment provided by the CNG. We have invented a CNG fuel injector which represents a significant improvement over presently known injectors which incorporates an improved valve needle having reduced needle mass and providing low noise on closing.